No. 25 balances both technical and lyrical elements, focusing on the middle register. Suggested tempo is dotted quarter=88, but this etude can also work at a slower tempo. One excellent resource for advice on Kopprasch and other etude collections is The Horn Handbook, by Verne Reynolds.  Though no longer in print, this book is well worth tracking down at a local public or university library. Concerning this etude, Mr. Reynolds writes that

Etude No. 25, in spite of its key signature and accidentals, is an excellent etude for horn in E as well as other transpositions. Try seeing how much of this etude can be played from memory in F after having worked it out in several other transpositions not including F. [p. 60]

One other suggestion would be to try B-flat horn fingerings for some of the passages below the staff.  Learn these passages on both F and B-flat fingerings, but ultimately the B-flat side may give better accuracy and clarity.